1. Field of the Invention
This invention relates to a flexible shaft for motion transmission along a curve.
More particularly, this invention relates to a flexible shaft for the transmission of rotary-to-rotary motion with a substantial permissible range of deviation of the angular relation between the rotary input and output axes.
2. Description of the Prior Art
There are many prior art patents having to do with flexible shaft devices.
U.S. Pat. No. 2,717,146, for example, teaches a flexible pipe for oil wells and the like. The pipe is made flexible by cutting a length of pipe into a multiplicity of interconnecting dovetailed tooth segments. The flexible pipe, with interlocked male and female segments, while it is axially flexible, each segment may be rotated one within the other. The distance the segment can move within an adjacent segment is represented by the amount of material removed by the torch used to separate the segments. The amount of movement is, of course, additive from one segment to the next. With multiple segments the rotational "slop" in the overall flexible pipe is considerable.
The foregoing design is disadvantaged in that precise rotational control is not possible due to a significant lag in the transfer of rotational movement from one end of the pipe to the next.
Another disadvantage of this device is the inability to separate the segmented pipe to remove, for example, a broken segment in the "chain" of segments.
U.S. Pat. No. 1,866,714 describes a flexible shaft wherein the shaft consists of a multiplicity of individual interlocking members positioned between an input and an output shaft. A first embodiment of the invention teaches a series of interlinked segments. Each segment has a tongue on one end and a groove in the opposite end, the groove being oriented 90.degree. from the tongue. The interlocking portions have outwardly curving convex surfaces, thus providing single point contact between engaging surfaces.
Another embodiment of the same invention teaches interlocking segments housed within a flexible outer pipe. One segment includes cross-notches or channels at opposite ends of a first member thereof that interlocks with an adjacent cross-shaped male second member. A multiplicity of these members make up the length of the shaft. The engaging parts have outwardly curving or convex surfaces as was described relative to the first embodiment, thus providing single point contact for each tooth between male and female members.
This patent is disadvantaged in that any rotational resistance between first and second ends of the shaft will tend to axially separate the members, one from the other. The outwardly curving engaging surfaces of the interlocked members exert the separating force on the shaft. This undesirable force is especially prevalent where the outwardly curving surfaces are oriented in an axial direction. As the segments separate under a load, rotational slack is introduced in the shaft. Each segment then no longer fits into the other with close tolerances between engaging male and female parts.
The present invention obviates the foregoing disadvantages in that there is close fitting tolerances from one interfitting member to the next as long as some part of a male tooth is still engaged with a female notch or groove in an adjacent member. This design will accommodate for longitudinal movement without additional circumferential slack being induced.
Another advantage over the prior art is the ability to allow for longitudinal misalignment from an input axis to an output axis while maintaining structural integrity of the flexible shaft. Each individual segment is so structurally designed to equally divide the male and female sections, thus providing equal strength from one part of the segment to the next. There is no "weak link" in the segmented shaft to worry about if the flexible shaft is constructed within the teaching of the present invention.